This application claims priority from JP2002-380497 filed Dec. 27, 2002, the contents of which are incorporated herein by reference thereto.
1. Field of Invention
The invention relates to a drive unit making use of an electric motor as a power source, and more particularly, to cooling and lubricating techniques in drive units for electric motorcars and hybrid drive units.
2. Description of Related Art
Because electric drive units, with an electric motor as a drive source, of a vehicle make use of as small electric motors as possible in conformity with a drive load at the time of normal running. When the motors are operated in a high loaded state, i.e., when a drive load is large, cooling is required to counter the generation of heat specifically at the time of high load. Applicant of this application has proposed a technique of cooling an electric motor by means of a working oil (ATF: automatic transmission fluid), which is circulated in a drive unit casing to lubricate and cool respective mechanisms of the electric drive unit, in a preceding application (JP-A-2001-238406).
The technique thus proposed provides an oil reservoir on a feed oil passage of a working oil so as to preferentially cool the working oil, which has absorbed heat, in one location. A cooling water passage is in contact with the oil reservoir. The resultant configuration, in which the working oil for cooling an electric motor is supplied, dripping from an oil reservoir provided in an upper area of the drive unit casing, and the hydraulic pressure in the oil reservoir is held down to balance the pressure on a side of the cooling water passage.
Incidentally, the technique thus proposed makes use of oil reservoirs as means for distribution of an oil flow to an electric motor for cooling, and of an oil flow to respective mechanisms for both lubrication and cooling, and so adopts a configuration, in which amounts of the oil discharged from the oil reservoirs are orifice-controlled in respective discharge oil passages. Although such orifice-control functions effectively at the time of normal temperatures at which a working oil has favorable flowability, oil flows in discharge oil passages on a side (for example, a side, on which respective mechanisms are lubricated) on which the orifices are large in diameter, are extremely increased relative to discharge oil passages on a side (for example, a side, on which an electric motor is cooled) on which the orifices are small in diameter, in a state in which flowability is sharply worsened due to an increase in viscosity at the time of very low temperature below xe2x88x9220 to xe2x88x9230xc2x0 C., so that an amount of an oil supplied to a region, to which an oil is supplied from the discharge oil passages on the side, on which orifices are small in diameter, is insufficient.
Hereupon, it is an object of the invention to provide an electric drive unit, which relies on orifice control and can discharge a working oil from oil reservoirs in a well-balanced manner all during the time of normal temperature and very low temperatures to perform cooling of an electric motor and lubrication and cooling of respective mechanisms.
In order to attain the above object, the invention provides an electric drive unit comprising an electric motor, a feed oil passage, which is provided in a casing of the drive unit and through which a working oil for cooling and lubrication is supplied to respective mechanisms of the drive unit including the electric motor, and an oil reservoir provided in an upper area of the casing of the drive unit to be communicated to a supply source of the working oil, and wherein the oil reservoir comprises a weir between a first reservoir, which is in communication with the supply source of the working oil and a first discharge oil passage, and a second reservoir in communication with a second discharge oil passage.
With the above structure, a configuration is effective in which the first discharge oil passage is opened above a coil of the electric motor through a first orifice, and the second discharge oil passage is in communication with an in-shaft oil passage of the electric motor leading to the respective mechanisms. Further, a configuration is effective in which the second discharge oil passage comprises a second orifice having a larger opening area than that of the first orifice. In this case, a configuration is effective in which the weir comprises an opening providing communication between the first reservoir and the second reservoir to guarantee supply of the working oil to the in-shaft oil passage of the electric motor. In this case, it is desired that the opening be composed of a first opening, having a larger opening area than that of the first orifice, and a second opening, having a larger opening area than that of the first opening, the second opening being arranged above the first opening at the time of being mounted on a vehicle. Further, it is desired that an opening of the first discharge oil passage in the first reservoir be arranged below a second opening of the weir at the time of being mounted on a vehicle. Furthermore, it is desired that the opening of the first discharge oil passage in the first reservoir be arranged above the first opening of the weir. Also, the opening area of the second orifice is set on the basis of the viscosity of the working oil in a cold state and pressure resistance of the oil reservoir. Also, a configuration is effective in which the oil reservoir contacts with a cooling medium flow passage with a heat transfer wall therebetween.
With the structure of a first aspect according to the invention, discharge of the working oil to the second discharge oil passage from the second reservoir is restricted until the working oil supplied from the supply source of the working oil to be accumulated in the first reservoir reaches a level to go over the weir in the oil reservoir, so that it is possible to rapidly accumulate a working oil in the oil reservoir even in a state, in which a working oil is bad in flowability at the time of very low temperature, while ensuring discharge of a working oil into the first discharge oil passage. Accordingly, with such arrangement, an oil level in the oil reservoir can be elevated to a level in a normal state even at the start, in very low temperatures, with the result that a working oil can be smoothly supplied to the first and second discharge oil passages.
Subsequently, with the structure of a second aspect according to the invention, the first orifices restrict discharge of a working oil from the first discharge oil passages whereby it is possible to expedite the rise of an oil level in the first reservoir even at the start, in very low temperatures, while ensuring the supply of a working oil to that side of the motor, which requires a small amount of supply and is to be cooled, thereby enabling expedited lubrication of the respective mechanisms, which requires a large amount of supply, and supply of a working oil to a side being cooled.
Subsequently, with the structure of a third aspect according to the invention, even when an oil level in the oil reservoir rises to place the oil reservoir in a filled state, the second orifice is used to adequately ensure discharge of a working oil from the second discharge oil passage in the same manner as at the time of a normal temperature, so that it is possible to suppress a pressure rise in the oil reservoir.
Also, with the structure of a fourth aspect according to the invention, because a working oil is discharged to the second discharge oil passage through the opening of the weir also in a state in which an oil level in the oil reservoir is not over the weir, supply of a working oil to lubricating portions of the respective mechanisms and the side being cooled is ensured.
Also, with the structure of a fifth aspect according to the invention, oil can also be supplied to the second discharge oil passage from the first opening before the accumulation of oil in the first reservoir has finished.
Also, with the structure of a sixth aspect according to the invention, oil can be surely supplied to the first discharge oil passage before a large amount of oil is supplied to the second reservoir from the second opening.
Also, with the structure of a seventh aspect according to the invention, even when an oil level in the oil reservoir is so low as not to be able to supply oil for cooling to the first discharge oil passage, oil can be supplied from the first opening, so that a minimum supply of a working oil is ensured to be supplied to the lubricating portions of the respective mechanisms.
Also, with the structure of a eighth aspect according to the invention, even when an oil level in the oil reservoir rises to place the oil reservoir in a filled state, the second orifice is used to adequately ensure discharge of a working oil from the second discharge oil passage even in a state of bad flowability at the time of a very low temperature, so that it is possible to suppress a pressure rise in the oil reservoir. Also, restriction on the flow with the weir makes it possible to prevent that insufficiency in discharge of a working oil toward the first discharge oil passage, which is caused by making the second orifice large.
Also, with the structure of a ninth aspect according to the invention, heat exchange with a cooling medium through the heat transfer wall in the oil reservoir, in which a working oil circulating in the drive unit casing accumulates, enables preferentially cooling a working oil whereby it is possible to efficiently cool the motor and the respective mechanisms. At that time, because pressure rise in the oil reservoir is suppressed, even at the time of very low temperature, seal leakage between the oil reservoir and the cooling medium flow passage, which contact with each other, is prevented whereby it is possible to prevent a cooling medium from being entrained into the working oil.